Background art of the technical field can be found in Japanese Unexamined Patent Application Publication No. 2012-238628 (Patent Literature 1). This literature describes that “it is an object of the invention to provide a high-temperature superconducting magnet capable of detecting with a high accuracy a voltage at which a quench occurs which corresponds to a normal conduction transition phenomenon of a superconducting coil and thereby quickly detecting an occurrence of the quench and performing a protective operation, in which the occurrence of the quench is detected by winding the superconducting magnet with a parallel conductor constituted by electrically connecting constituent conductors each other by at least two points, arranging voltage terminals at a superconducting wire rod in each section of the electrically connected parallel conductor, and observing the potential difference.”
Moreover, there is also Japanese Unexamined Patent Application Publication No. Hei 8(1996)-304271 (Patent Literature 2). This literature describes that “aiming at providing an apparatus and a method for detecting a quench occurrence capable of sensing a minute change thereof and observing the change of a whole system at an initial stage of the quench occurrence, the apparatus for detecting the quench of a superconducting wire rod detects by using an optical fiber wound around the superconducting wire rod, a light source emitting a deflected beam into the optical fiber, and a device that detects a polarization from the optical fiber.”